telephone bandwidth

[Dale, Philip S.]

This is something of a "trivia quiz" question, but the answer would be quite
useful to us.

It's well known that the telephone system utilizes a narrow frequency
bandwidth, an early decision made to maximize the number of conversations
that could be carried. But what is the actual cutoff? I - and everyone I've
checked with - has the vague memory that it's around 3000-3200 Hz, but no
one can find an actual written reference to this. Can anyone help?

For extra credit, how do the British and U.S. telephone systems compare in
this regard?

Many thanks,
Philip Dale